This invention relates generally to transport systems for ribbons, tapes, and web structures, and more particularly, to a transport system which supplies a ribbon-like structure to a movable utilization head.
The rapid acceleration and deceleration of tapes or other ribbon-like structures has been a problem in the design and operation of various types of electromechanical equipment. One type of equipment which has long been plagued by engineering problems associated with pulsed ribbon usage is in the field of tape recording devices, particularly of the type which store and supply data for use by electronic computers. Such devices are generally required to transmit data to an electronic computer, and receive data to be recorded, while the tape or ribbon is transported across the magnetic heads at greater than a predetermined minimum speed. Such a speed requirement produces waste of the tape because no data recording or transmission can be performed during the time that the tape is being accelerated to the predetermined minimum speed. Moreover, since such devices cannot stop the tape instantaneously, the length of tape which is transported by the heads while the tape is decelerating to a stop is also wasted.
The prior art has provided arrangements for reducing the acceleration and deceleration times of tape. In a known system, the tape is drawn by a vacuum into a storage chamber where a predetermined length of the tape is stored. In operation, the tape is moved through the vacuum chamber to meet the demands of utilization at the tape heads. However, a predeterminable length of the tape is maintained in the vacuum chamber so as to form a buffer between a ribbon reel and the utilization head. Thus, when the tape which is transported across the heads is desired to be accelerated or decelerated quickly, the tape reels, which are substantial inertial masses, need not be stopped and started with equal acceleration. Thus, acceleration and deceleration can be achieved in a much shorter time, resulting in a substantially reduced waste of the tape.
In some known tape recording arrangements, the tape is stored in vacuum chambers on either side of the utilization head. By this provision, the system is made bidirectional such that the tape can be transported past the tape head in either direction.
Many of the problems discussed hereinabove are applicable to printers. However, printers have different operating characteristics from tape recording machines, many of which raise problems which are not solved by the aforementioned known vacuum buffering systems. A first major problem-raising difference between printers and tape recording machines is that the printing carriage of a printer is moved along a fairly long printing path during operation. Clearly, it is more difficult to supply a ribbon to a moving printing carriage than to a stationary magnetic head. For this reason, almost all commercially successful serial impact printers have approximated the situation of a tape recording machine by installing the ribbon supply and take-up reels directly onto the carriage. It is a problem with such known moving ribbon reel arrangements that as the printing carriage is moved to each subsequent printing location, and stopped thereat so that the printing head on the carriage can perform the printing function, the overall mass of the arrangement, including the ribbon reels, which must be stopped and started at each print location, is a limiting factor in achieving high printer speed.
A further distinction between a printer and a tape recording machine is that a printer utilizes its ribbon while the ribbon is stopped. Moreover, each utilization of the ribbon, at each printing location, consumes the ink on the ribbon thereby requiring a fresh section of ribbon to be interposed between the printing element and the paper to be printed for each printing operation. There is, therefore, no alternative in a printer but to stop and start the ribbon, unlike the situation of the tape recording machine where the tape could be run continuously if waste could be tolerated. There is, therefore, a pressing need for a ribbon supply arrangement for a printer which can rapidly accelerate and decelerate the ribbon.
As the rate of operation of printers is advantageously increased, it is intuitively obvious that the rate at which the ribbon is transported and consumed is also increased. There is therefore a need for supplying printers with greater amounts of ribbon so as to increase the duration of the time interval between ribbon changes. Such greater amounts of ribbon, however, cannot be supplied without increasing the overall mass of the ribbon supplied in the printer. In the known printers, the increased ribbon mass renders the required stopping and starting of the carriage more difficult. Moreover, the starting and stopping of the ribbon to provide fresh ribbon for each subsequent printing function is also rendered more difficult in view of the increased mass and momemnt of inertia of the enlarged ribbon reels.
In addition to the foregoing, ribbons of the type used in printers are entirely distinguishable from magnetic recording types insofar as they are provided with a frangible ink coating on one side which is easily broken and removed. Thus, unlike magnetic tape which can be handled firmly on either side, such as by interposing it between a capstan and a pinch roller, such treatment of a printing ribbon would result in at least partial removal of the ink coating, causing ink particles to be distributed within the machine. Of course, print quality is also degraded when a ribbon which is only partially coated with ink is used.
It is still a further distinction between tape recording machines and printers that printers mechanically deform the ribbon during usage. The application of an impact force, illustratively in the shape of a fully-formed character, causes a physical deformation of the ribbon. Such a deformation has the effect of increasing the effective thickness of the ribbon, thereby creating difficulty in taking-up the used ribbon on a reel having the same diameter as the supply reel. The take-up reel tends to fill to capacity before the supply reel is exhausted of ribbon.
It is, therefore, an object of this invention to provide a ribbon transport arrangement which can be provided with a larger supply of ribbon than known arrangements without adding undue mass to a printing carriage which is moved discontinuously.
It is a further object of this invention to provide a ribbon transport arrangement which is supplied with a greater amount of ribbon than known arrangements, but which reduces the effect of ribbon and its supporting structure upon the printing carriage.
It is also an object of this invention to provide a ribbon transport arrangement which can accelerate and decelerate a film or fabric ribbon in less time than known ribbon transport arrangements used in printers.
It is still a further object of this invention to provide a ribbon transport arrangement which can accommodate for deformities in the ribbon resulting from impact printing.
It is still another object of this invention to provide a ribbon transport system for transporting a ribbon of the type which is coated on one side with a printing ink; the ribbon transport system communicating with the ribbon only via the reverse, uncoated side thereof.